1. Field of the Invention
The present invention generally relates to the field of sensors and their applications. More particularly, the present invention relates to optical sensors used in turbulence measurements.
2. Description of the Related Art
Most fluid flows, including water air and gas flows are turbulent and therefore characterized by a wide range of coexisting scales of motion, from fraction of millimeter to meters or even kilometers. Increased turbulence in a fluid flow results in an increase in energy dissipation, mixing, heat transfer and drag experienced by an object moving through the fluid. In a three dimensional fluid flow, turbulent kinetic energy (TKE) is produced by large-scale forcing such as shear stresses, buoyancy effects, waves, pressure etc. TKE is the mean kinetic energy per unit mass associated with eddies of all scales of the flow. Intensity of turbulence can be derived from TKE. TKE is one of the most fundamental parameter in turbulence measurement.
Because of the ubiquity of turbulent flows in everyday experience, detection and measurement of turbulence plays a crucial role in human lives as well as in engineering and science. The applications of turbulence measurement techniques are as vast as the ubiquity of turbulent processes—for example: airplanes safety, weather forecast, climate prediction, hurricane forecasting, sewage and water management systems, oceanography, wind turbines, and so forth.
Turbulence plays a crucial role in transport of the heat, momentum, and energy of the ocean and the atmosphere. Oceanic turbulence measurement attempts date back to 1950s, when researchers first developed profilers/sensors to detect the presence of submarines in the ocean. Since then, many oceanographic sensors have been developed and their use has revealed numerous features of oceanic processes. In addition, a number of SONAR techniques have also been developed for oceanic turbulence measurements.
U.S. Pat. No. 7,283,426, assigned to BAE Systems Information and Electronic Systems Integration Inc. discloses a heterodyne method for detecting, tracking and locating submarines by utilizing pulsed coherent radiation from a laser projected down a water column. Flow rate is obtained by correlating it with the flow mean quantity. The output is a characterization of particle movement which in turn is used for detecting and tracking submarines. This is an indirect method of turbulence characterization. It is believed that this method would not be applicable in the absence of oceanic particles. Further, the method is applicable to oceanographic turbulence detection only; it does not seem to be applicable in other forms of turbulence measurements, for example, in air turbulence measurement.
Existing oceanographic turbulence sensors directly measuring turbulent parameters, such as those developed by Rockland Scientific Inc., use modified piezoelectric sensors. These sensors entail high cost of manufacturing and maintenance. They also require mean steady flow of water for accurate turbulence measurement. The sensor is too fragile to be used in high speed applications and under rough weather conditions. In addition, the sensor cannot be used if the sensor is not moving through the flow.
Wake turbulence is the turbulence that forms behind an aircraft as it passes through the air. It is especially hazardous during the landing and take-off phases of flight, and therefore measurement of wake turbulence plays an important role in successful designing of aircrafts and their hazard prevention systems. A number of commercial techniques have been developed for air turbulence measurement in aircrafts. Examples of these techniques include Doppler Light Detection and Ranging (LIDAR), interferometers, bistatic radars, and so forth. These techniques also suffer from one or more disadvantages of existing systems discussed above.
In light of the foregoing, there exists a need to provide a direct method and system for detecting and measuring turbulence in a turbulent environment. The method should be versatile, direct, and noninvasive, i.e., it should be applicable for a number of turbulent environments and physical or weather conditions. Moreover, the system should be able to measure various turbulence related parameters with minimal data processing.